1. Field of the Invention
The present invention relates to the field of display technology, and more particular to an inverted quantum dot light-emitting diode (QD-LED) and a manufacturing method thereof.
2. The Related Arts
With the continuous development of the display technology, people increasingly demand higher and higher quality of displaying. Quantum dots (QDs) are nanometer semiconductor particles in the form of spheres or similar to spheres made of elements of II-VI groups or III-V groups, having a particle size between several nanometers and tens of nanometers. Since the particle size of QDs is less than or close to the exciton Bohr radius of the corresponding body material, an quantum confinement effect is generally involved, where the energy band structure is changed from quasi-continuity of the body material to the discrete structure of the quantum dot material, making the quantum dots exhibiting unique behavior of stimulated emission of light. When the size of the QDs is decreased, the energy band gap becomes increased so that the energy required for exciting the QDs and the energy released from the excited QDs returning back to the ground state are increased correspondingly, exhibiting a “blue-shifting” phenomenon of the excitation of the QDs and the fluorescent spectrum. By controlling the size of the QDs, the emission spectrum thereof may be made covering the entire range of visible light. For example, when the size of cadmium selenide is decreased from 6.6 nm to 2.0 nm, the luminescence wavelength “blue-shifts” from red light zone of 635 nm to blue light zone of 460 nm.
Quantum dot materials have advantages, such as concentrated luminescence spectrum, high color purity, and luminescence color being easily adjustable through the size, structure, or composition of the quantum dot materials. Such advantages allow for applications in display devices to effectively improve the color gamut and color restorability of the display devices.
Quantum dots of a core-shell structure show extremely high luminous efficiency, adjustable luminescent spectrum, and extremely narrow half-peak width and also demonstrate better photo-chemical stability and applicability to solution based manufacturing processes, and are thus makeable on a flexible backing to form a QD-LED. A typical inverted QD-LED is generally made up of a cathode, an electron transport layer (ETL), a QD emissive layer, a hole transport layer (HTL), a hole inject layer (HIL), and an anode that are stacked in sequence from bottom to top. Inverted QD-LEDs that are currently available and demonstrate better performance are of organic-inorganic hybrid structures, in which the HTL and the HIL are both organic materials, while the ETL is inorganic metal oxide, such as nanometer particles of ZnO or TiO2. Although ZnO or TiO2 provide excellent electron transport speeds, yet the nanometer particles show poor property of dispersion and are unstable, making them easy to aggregate and thus leading to lowering of electron transport rate and directly resulting in inhomogeneity of a film surface, thereby limiting the luminous efficiency of a device and reducing the life span of the device.